(1) Field of the Invention
This invention relates to a high-frequency inductor comprising a conductive land formed on an insulating substrate, especially an inductor realizing a high value of the Q factor, and to a manufacturing method of such an inductor.
(2) Description of the Prior Art
FIG. 1 shows a conventional high-frequency inductor used for a microwave circuit or the like; and FIG. 2 is a cross sectional view thereof.
A high-frequency inductor 20 comprises an insulating substrate 21, a spiral conductive land 22 formed on a surface of the substrate 21, and terminal electrodes 23a and 23b along opposed side ends of the substrate 21. An outer end 22a of the spiral conductive land 22 is connected with the terminal electrode 23a, and an inner end 22b is connected with the terminal electrode 23b. The conductive land 22 and the terminal electrodes 23a and 23b are covered with an insulating film 24, which has a connecting electrode 25 formed thereon. An end of the connecting electrode 25 is connected to the inner end 22b through a through-hole electrode 26, and the other end of the connecting electrode 25 is connected to the terminal electrode 23b, whereby the inner end 22b and the terminal electrode 23b are connected to each other.
The inductor 20 having the above construction is manufactured in the following way. The insulating substrate 21 is coated with a metal film by sputtering, evaporation or the like. Then, the metal film is photo-etched, whereby the spiral conductive land 22 and the terminal electrodes 23a and 23b are formed. The terminal electrode 23a and the outer end 22a are connected to each other. The insulating substrate 21 having the spiral conductive land 22 and the terminal electrodes 23a and 23b is coated with polyimide to form the insulating film 24. A portion of the film 24 corresponding to the inner end 22b is hollowed to make a through hole; and portions of the film 24 corresponding to the terminal electrodes 23a and 23b are removed. The insulating film 24 is coated with a metal film, which is then photo-etched to form the connecting electrode 25 and the through-hole electrode 26.
The above conventional inductor has a problem of having a low value of the Q factor due to a large resistance value. This occurs because the conductive land and the terminal electrodes are manufactured by the thin film technologies such as sputtering and evaporation.
This problem can be solved by increasing the thickness of the conductive land and the terminal electrodes. However, a thicker metal film takes longer to etch. If the etching lasts a long time, the metal film is etched not only vertically but horizontally. As a result, even a portion 30 (FIG. 3) which should be left to be the conductive land or the terminal electrode is etched, despite being the portion 30 covered with a mask 28. Consequently, the value of the Q factor is decreased, or the formation of the spiral conductive land cannot be realized.